title: Stress-induced cytokinin synthesis increases drought tolerance through the coordinated regulation of carbon and nitrogen assimilation in rice.
abstract: The effects of water deficit on carbon and nitrogen metabolism were investigated in flag leaves of wild-type and transgenic rice (Oryza sativa japonica 'Kitaake') plants expressing ISOPENTENYLTRANSFERASE (IPT; encoding the enzyme that mediates the rate-limiting step in cytokinin synthesis) under the control of P(SARK), a maturation- and stress-induced promoter. While the wild-type plants displayed inhibition of photosynthesis and nitrogen assimilation during water stress, neither carbon nor nitrogen assimilation was affected by stress in the transgenic P(SARK)::IPT plants. In the transgenic plants, photosynthesis was maintained at control levels during stress and the flag leaf showed increased sucrose (Suc) phosphate synthase activity and reduced Suc synthase and invertase activities, leading to increased Suc contents. The sustained carbon assimilation in the transgenic P(SARK)::IPT plants was well correlated with enhanced nitrate content, higher nitrate reductase activity, and sustained ammonium contents, indicating that the stress-induced cytokinin synthesis in the transgenic plants played a role in maintaining nitrate acquisition. Protein contents decreased and free amino acids increased in wild-type plants during stress, while protein content was preserved in the transgenic plants. Our results indicate that the stress-induced cytokinin synthesis in the transgenic plants promoted sink strengthening through a cytokinin-dependent coordinated regulation of carbon and nitrogen metabolism that facilitates an enhanced tolerance of the transgenic plants to water deficit.
authors.affiliation: Department of Plant Sciences, University of California, Davis, California 95616.
authors.forename: Maria
authors.initials: M
authors.lastname: Reguera
authors.forename: Zvi
authors.initials: Z
authors.lastname: Peleg
authors.forename: Yasser M
authors.initials: YM
authors.lastname: Abdel-Tawab
authors.forename: Ellen B
authors.initials: EB
authors.lastname: Tumimbang
authors.forename: Carla A
authors.initials: CA
authors.lastname: Delatorre
authors.forename: Eduardo
authors.initials: E
authors.lastname: Blumwald
mesh_terms: D000222:Adaptation, Physiological; D019883:Alkyl and Aryl Transferases; D000596:Amino Acids / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D003583:Cytokinins / Q000096:biosynthesis*; D003681:Dehydration; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D053858:Metabolic Networks and Pathways; D055442:Metabolome; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010084:Oxidation-Reduction; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D055550:Protein Stability; D013312:Stress, Physiological
chemical_list: D000596:Amino Acids; D003583:Cytokinins; D010940:Plant Proteins; D002244:Carbon; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase; D009584:Nitrogen